Construction Sediment:
The Greatest Threat to Water Quality
Raymond Slade, Jr.,
Certified Professional Hydrologist
Organization of presentation
• Introduction --how construction sediment contaminates water resources
• The Threat --why construction sediment is the greatest threat to water quality
• Contamination Examples --Central Texas examples of water resource contamination from construction sediment
• Local Controls --construction controls most used in Texas
• Available Controls --construction controls used throughout the U.S.
• Model Ordinances --existing and model construction sediment ordinances
• Additional Information --references and sources for more information
Beginning of each section designated by blue type at top of slide
Introduction
Construction typically involves building highways, roads, structures, parking lots, utility lines, and work access roads. Soils are disturbed and vegetation often removed during construction. Many tons of
loose sediment typically are created during this process.
Rainfall and wind then often transport tons of sediment to
receiving streams, reservoirs, and aquifers, causing water
quality degradation. Additionally, vegetation attenuates much
of the contaminants in overland flow, thus its removal causes
additional water-quality degradation of receiving streams.
Because of the facts presented on the next 5 slides, many earth scientists, including the author of this presentation, deem construction sediment to represent
the greatest single threat to water resources.
Sediment in Barton Creek flood through Barton Springs pool
The Threat
Threat 1. Sediment is the only water-quality
contaminant that exists throughout all stream basins.
Within a few hours, a single small construction site can generate a sediment load sufficient to contaminate
entire receiving streams, lakes, and aquifers.
Sediment from construction of motel on Lady Bird Lake
Threat 2. Along with sediment, typical construction site pollutants include fluids from construction equipment, adhesives, paints, cleaners, masonry, cement, fertilizers, pesticides, and wastes from electrical, plumbing, heating, and air conditioning installations.
Bee Cave Galleria in Barton Creek basin
Pesticide washed into creek from improperly stored bags
Dead fish in
receiving stream
Example of pesticides in runoff from Bee Cave Galleria development in the Barton Creek basin.
Threat 3. Many studies throughout the Nation
document sediment loads to be as much as 1000 times
greater from construction sites than from static land
use sites.
Threat 4. Degradation of water quality from
construction sediment often is severe enough to limit or even prohibit water use and often kills biological species and vegetation in receiving waters.
Sediment
plume
Threat 5. Expensive remedial action sometimes can remove sufficient volumes of deposited and
suspended sediment in order to restore limited water use. However preventive action usually is much
cheaper than remedial action and aquifers and many ponds and reservoirs cannot be restored.
Dredging and pumping to remove sediment
Removing deposited sediment from stream
Construction site runoff Environmental Impacts
• Transports toxic pollutants and nutrients
• Turbidity limits sunlight penetration and photosynthesis
• Reduces oxygen availability
• Clogs fish gills
• Fills spawning and breeding grounds
• Smothers bottom Communities
• Reduces visibility for feeding and upsets food chain
Effect of erosion and sediment controls on suspended sediment concentrations
Construction site condition
Data from Piedmont, Ca.
A BMP is a “Best
Management Practice”
Dozens of studies throughout the Nation document erosion rates from natural areas (established urban, forest, rangeland) to be less than 1.0 ton per acre per year.
Many dozens of other studies document erosion from construction sites to range from 7.2 to greater than 1,000 tons per acre per year.
--EPA 840-B-92-002 report
Central Texas examples of water resource contamination from construction sediment
The following slides present 5 examples where construction sediment has contaminated streams, ponds, and springs in Central Texas. For each example, the construction site
represented only a very small part of the watershed area that provides runoff to the contaminated site. Each of these
instances of sediment contamination could have been prevented with proper control measures.
Contamination Examples
Throughout much of 1980, sediment in runoff from the construction of Barton Creek Square Mall entered Barton Creek and discharged from Barton Springs within hours of many rainfall events. The
sediment concentrations at the Springs were so great that the springs pool had to be closed during such events.
Sediment in water sample from Barton Springs
The mall covers about ¼ square mile and Barton Springs flow comes from about 350 square miles yet
construction sediment from the mall was so great that visibility in the
pool approached zero.
Measure of turbidity from sediment
during storm
Barton Springs
Lick Creek
Green Hole on Lick Creek, West Travis County, Summer 2003
Green Hole on July 27, 2004,
after rainfall caused overflow
from the West Cypress Hills
subdivision detention pond for
development construction
Dead Mans Hole on Dead Mans Creek, North Hays County, before construction of a small dam in the watershed in Spring 2005
Dead Mans Hole after construction of the dam
Dead Mans Creek
Hamilton Pool, West Travis County, prior to June 2007
Road cut for land development in
Hamilton Creek basin began June, 2007
Hamilton Creek
Hamilton Creek (cont.)
Road cut along Hamilton Creek
Hamilton Pool after a small storm flushed construction sediment to the pool
Bee Creek
Bee Creek near Hwy 71, West Travis County, prior to development in basin
Bee Creek, August 2007, immediately after development began in basin
Construction controls most used in Texas
Silt fences which often fail during large storms
Local Controls
April 2007 photograph of sediment-saturated runoff from the
AMD construction site, fouling stream waters with mud that
was supposed to be stopped by a silt fence
Could this be the next construction sediment problem?
Construction of the Rocky Creek Ranch subdivision on the south side of Hamilton Pool Road about 4.5 miles west of Highway 71. The photo shows the clearing, cutting and filling pursuant to the first phase of development on the east side of Rocky Creek (a tributary of Barton Creek). June 2008 photo
A better silt fence
www.stormwatercenter.net/Slideshows/ESC.htm
Available controls
Construction controls used throughout the U.S.
1. Minimize Clearing 2.a. Protect Waterways
Buffers and special crossings for waterways 2.b. Stabilize Drainageways
Checkdams, sod, erosion control blankets, rip rap 3. Phase Construction
4. Rapid Soil Stabilization
hydroseed, mulch, erosion control blankets 5. Protect Steep Slopes
6. Perimeter Controls
Earth dikes, diversions, silt fences, stabilize construction entrance 7. Employ Advance Settling Devices
sediment traps & sediment basins 8. Certified Contractors Implement Plan 9. Adjust Plan as Field Conditions change 10. Assess and Revise Practices After Storms
Repair damage, modify practices, reinforce, cleanout
http://www.stormwatercenter.net/Slideshows/ESC.htm Note: Most of these practices are not commonly used in Texas
Available sediment construction controls
Slope protection hay mulching
Hydroseeding operation Hay mulch
ground cover Use of mats to minimize erosion
Available sediment construction controls (cont.)
Sedimentation basin with standpipe
Checkdams
Berm dividing multi-cell sedimentation basin
Available sediment construction controls (cont.)
Swale to divert runoff around construction site in non-erosive manner
Mats and hay to stabilize channel
Rock to stabilize channel
Bonded Fiber Matrix
Bonded Fibre Matrix has been reported to be a very effective product for controlling erosion, especially on steep slopes. It is a unique class of
hydroseeding erosion control product, a hydraulically applied product that does the job as well as or better than erosion control blankets. The matrix is a continuous layer of elongated fiber strands held together by a water-
resistant bonding agent. It keeps raindrops from hitting the soil because it has no holes larger than one millimetre. It allows no gaps between the
product and the soil. It has a high water-holding capacity. It will not form a water-insensitive crust that can inhibit plant growth. It biodegrades into materials that help plant growth (Wikipedia).
Model Ordinances
Existing and model construction sediment ordinances
Many cities, counties, states and other governmental agencies have adopted ordinances that address all aspects of contamination from construction. Many such ordinances are presented by the Stormwater Center at
http://www.stormwatercenter.net/
Click on “ordinance” on left side of page
Selected recommendations for construction sediment control in the Hill Country Area
• A phased plan for simultaneous construction should be prepared and approved by a licensed engineer or other specialist
• The size of the disturbed area under construction should be no greater than that for which sediment in runoff from a 10-year storm would be contained on site.
• A licensed engineer or other specialist should design and approve the plan and practices for construction sediment control to assure the above.
• A licensed engineer or other specialist should be responsible for inspection and maintenance of the construction sediment controls and plan throughout the construction period.
The Stormwater Center presents a model ordinance for controlling construction sediment at
http://www.stormwatercenter.net/
Model%20Ordinances/esc_model_ordinance.htm
I. Introduction/ Purpose II. Definitions
Permits
Review and Approval
Erosion and Sediment Control Plan III. Design Requirements
Clearing and Grading Erosion Control
Sediment Controls
Waterways and Watercourses Construction Site Access
IV. Inspection V. Enforcement
Stop-Work Order; Revocation of Permit Violation and Penalties
Major components of the ordinance:
Another model ordinance for erosion control is presented on the Internet by the EPA at
http://www.epa.gov/owow/nps/ordinance/mol2.htm
Keeping Soil in Its Place:
A Presentation on Erosion and Sediment Control (ESC)
is online at
http://www.stormwatercenter.net/Slideshows/ESC.htm
Additional Information
References and sources for more information
Slideshows with additional information on stormwater management
• Why watersheds
http://www.cwp.org/whywatersheds_files/frame.htm
• Impacts of urbanization
http://www.stormwatercenter.net/Slideshows/impacts%20for%20smrc/
sld001.htm
• Better site design
http://www.stormwatercenter.net/Slideshows/bsd%20for%20smrc/sld0 01.htm
• Eight tools for watershed protection
http://www.stormwatercenter.net/Slideshows/8tools%20for%20smrc/sl d001.htm
• Stormwater Best Management Practices
